Burner installations and methods of commissioning and operating burner installations

ABSTRACT

A burner installation includes a stack, a burner, a fuel valve, an air valve and a control device including a store storing burner pairs of values of air and fuel valve settings at firing rates and for controlling air and fuel valve settings. A stack flow regulator adjusts flow of combustion products through the stack and a pressure sensing arrangement monitors pressure of combustion products downstream of the burner. Respective pairs of stack flow regulator setting values and a measured value from the pressure sensing arrangement are stored for pairs of air and fuel valve settings values. The control device receives a feedback signal from the pressure sensing arrangement for comparing an actual pressure value with a stored pressure value and to trim the stack flow regulator setting to cause the actual pressure value from the pressure sensing arrangement to move closer to the stored pressure value.

This application claims benefit of Ser. No. 1214740.1, filed 17 Aug.2012 in United Kingdom and which application is incorporated herein byreference. To the extent appropriate, a claim of priority is made to theabove disclosed application.

TECHNICAL FIELD

This invention relates generally to burner installations, to controlsystems for use in such installations and to methods of commissioningand operating burner installations. The invention relates in particular,but not exclusively, to a burner installation for a large boiler such asmight be used in hospitals, hotels, offices or other industrial,commercial or domestic premises.

BACKGROUND OF THE INVENTION

A known burner control system is described in GB2138610A, the disclosureof which is incorporated herein by reference. In that control system theflows of air and fuel are controlled by air and fuel valvesrespectively, and pairs of values of air and fuel valve settings arestored for varying firing rates of the burner. Those air and fuel valvesettings are stored during a commissioning procedure by a commissioningengineer who is able to adjust the valve positions to obtain idealcombustion conditions for a given firing rate. A control system of thiskind has been used for many years in the United Kingdom, the UnitedStates and elsewhere, being commercially available from AutoflameEngineering Ltd, for example as the Mk 7 Evolution MM control unit, andhas proved very successful.

Burner installations typically incorporate a stack, through which theproducts of combustion are discharged. Usually the stack is vertical anda back flue extends from the burner to the stack to transfer theproducts of combustion from the burner to the stack. Sometimes more thanone burner will be associated with the same stack. The conditions in thestack can affect the combustion at the burner. It has previously beenproposed to include a regulator valve in the flow of combustion productsand to control the position of the regulator valve with a servo motor inorder to try to maintain a constant draught. Such a control arrangementis unable to take account of a wide variety of parameters that mayaffect the desired draught. For example, different firing rates of aburner may desirably require different draughts to achieve optimumcombustion conditions and even at a given firing rate, other factors,for example ambient temperature, may still affect the most desirableposition of a stack regulator valve.

It is an object of the invention to provide an improved burnerinstallation and improved methods of commissioning and operating aburner installation.

SUMMARY OF THE INVENTION

According to the invention there is provided a burner installationcomprising a stack and a burner upstream of the stack for burning fuelin air to produce combustion products which are passed into the stack, afuel valve for adjusting the flow of fuel to the burner, an air valvefor adjusting the flow of air to the burner, a control device includinga store arranged to store pairs of values of air and fuel valve settingsat various firing rates of the burner and for controlling the air andfuel valve settings in dependence upon the stored air and fuel valvesettings, wherein the installation further comprises a stack flowregulator for adjusting the flow of combustion products through thestack, and a pressure sensing arrangement for monitoring the pressure ofcombustion products downstream of the burner, wherein the store isfurther arranged for storing respective pairs of values of the settingof the stack flow regulator and a measured value from the pressuresensing arrangement for the pairs of values of air and fuel valvesettings, and wherein the control device is arranged to receive afeedback signal from the pressure sensing arrangement for comparing anactual pressure value with a stored pressure value and to trim thesetting of the stack flow regulator to cause the actual pressure valuefrom the pressure sensing arrangement to move closer to the storedpressure value.

A burner installation of this kind is able to set different stack flowregulator settings at different firing rates of the burner. Furthermore,that setting can be further trimmed according to an actual pressurevalue measured in the flow of the combustion products to bring thatpressure value closer to a stored value for that firing rate of theburner. In this way the effect of varying stack conditions on thecombustion in the burner can be very much reduced across a range offiring rates of the burner.

The stored values are preferably obtained during commissioning of theburner by a commissioning engineer who is able to select optimumsettings for the air and fuel valves, and the stack flow regulator at aparticular firing rate of the burner and also store a pressure valuefrom the pressure sensing arrangement, and repeat the exercise at otherfiring rates. The commissioning engineer is free to take any factor hechooses into account when selecting the values to store.

The fuel may be oil or gas and the fuel control valve may take anysuitable form. Similarly the air control valve may take any suitableform. As will be understood the purpose of the fuel and air valves is tocontrol the flow rates of fuel and air to the burner and any arrangementwhich achieves that and can be controlled may be adopted. For examplethe airflow may be controlled partly by adjusting an impeller. In aparticular example of the invention described below the burner is ableto be supplied with either oil or gas. The fuel and air valves are vanedvalves for example butterfly valves whose angular positions arecontrolled by servo motors.

The invention is able to be applied to a wide variety of flue and stackarrangements and in a variety of ways. In one example, the burnerinstallation may further comprise a flue for conveying combustionproducts from the burner to the stack. The stack flow regulator may bedisposed in various positions; in particular it may be disposed in theflue. Of course, since the flue leads to the stack, the adjustment ofthe flow through the flue adjusts the flow through the stack. The fluemay extend between the burner and the stack. The stack may extendapproximately vertically upwardly. The flue may include a verticalportion and/or an upwardly inclined portion. There may be more than oneburner, and therefore more than one flue, connected to the same stack.

The stack flow regulator may be of any suitable form for regulating theflow through the stack. The stack flow regulator may comprise a valvehaving one or more vanes. For example, in a relatively smallinstallation it may be a butterfly valve and in a larger installation itmay have two or more vanes which may be pivotally mounted. A servo motormay be provided for operating the valve.

The pressure sensing arrangement may sense one or more pressures in theflow of combustion products downstream of the burner. The pressuresensing arrangement may comprise a pressure sensor upstream of the stackflow regulator. A variety of pressure sensing arrangements may beadopted, but in an embodiment of the invention described below, thepressure sensing arrangement is a differential pressure sensingarrangement and is arranged to measure the pressure difference betweenthe pressure sensor upstream of the stack flow regulator and ambientpressure. In this embodiment, the pressure sensing arrangement isconnected to the control device to provide a pressure value representingthe difference in pressure measured between the pressure sensor upstreamof the stack flow regulator and ambient pressure.

According to the invention there is also provided a method of operatinga burner installation, including the following steps:

providing a burner installation comprising a stack and a burner upstreamof the stack for burning fuel in air to produce combustion productswhich are passed into the stack, a fuel valve for adjusting the flow offuel to the burner, an air valve for adjusting the flow of air to theburner, a control device including a store, a stack flow regulator foradjusting the flow of combustion products through the stack, and apressure sensing arrangement for monitoring the pressure of combustionproducts downstream of the burner,

storing, at various firing rates of the burner, pairs of values of airand fuel valve settings and associated pairs of values of a setting ofthe stack flow regulator and a measured value from the pressure sensingarrangement,

operating the burner and controlling the air and fuel valve settings andthe stack flow regulator valve setting in dependence upon the stored airand fuel valve settings and the associated stack flow regulator setting,

receiving at the control device a feedback signal of the actual pressurevalue from the pressure sensing arrangement,

comparing the actual pressure value from the feedback signal with astored pressure value, and

trimming the setting of the stack flow regulator to cause the actualpressure value from the pressure sensing arrangement to move closer tothe stored value.

The pressure sensing arrangement may measure the pressure differencebetween a pressure sensor upstream of the stack flow regulator andambient pressure, and the pressure difference may be the pressure valuefed back as a signal to the control device.

If it is desired to operate the burner at a firing rate between thestored settings, stored values can be interpolated. The control devicecan arrive at values for settings of the valves and the pressure valueby interpolating between stored values associated with a higher firingrate and a lower firing rate. Such operation in which interpolatedvalues are employed is within the scope of the invention.

According to the invention there is further provided a method ofcommissioning a burner installation, including the following steps:

(i) providing a burner installation comprising a stack and a burnerupstream of the stack for burning fuel in air to produce combustionproducts which are passed into the stack, a fuel valve for adjusting theflow of fuel to the burner, an air valve for adjusting the flow of airto the burner, a control device including a store, a stack flowregulator for adjusting the flow of combustion products through thestack, and a pressure sensing arrangement for monitoring the pressure ofcombustion products downstream of the burner,

(ii) adjusting the air and fuel valve settings to positions wheredesired combustion conditions are obtained for that, first, firing rateof the burner,

(iii) storing the pair of values of air and fuel valve settings thatprovide those combustion conditions,

(iv) adjusting the setting of the stack flow regulator to a positionwhere, for the first firing rate of the burner, the desired stack flowof combustion products is obtained,

(v) storing a value of the setting of the stack flow regulator and thepressure value from the pressure sensing arrangement with the values ofthe air and fuel valve settings, and

(vi) repeating steps (ii) to (v) above at other firing rates of theburner.

It should be understood that steps (ii) to (v) above are not necessarilycarried out in the same order in which they are listed.

The pressure sensing arrangement may measure the pressure differencebetween a pressure sensor upstream of the stack flow regulator andambient pressure, and the pressure difference may be the pressure valuestored.

As will be understood, the commissioning of the burner will be followedby operation of the burner. Commissioning will take place prior to anyoperation of the burner and may also take place at any desired timeafter a period of operation, for example as a result of somemodification to the burner installation or merely for routinemaintenance purposes. The commissioning method may thus include thefollowing subsequent steps:

operating the burner, controlling the air and fuel valve settings independence upon the stored air and fuel valve settings, and setting thestack flow regulator according to the value stored in association withthe air and fuel valve settings,

receiving at the control device a feedback signal of the actual pressurevalue from the pressure sensing arrangement,

comparing the actual pressure value from the feedback signal with thestored pressure value associated with the stack flow regulator settingvalue, and

trimming the setting of the stack flow regulator to cause the actualpressure value from the pressure sensing arrangement to move closer tothe stored value.

Whilst it is within the scope of the invention for the trimming of thesetting of the stack flow regulator to cause the actual pressure valuefrom the pressure sensing arrangement merely to move partway towards thestored value, it is usually preferred that the setting of the stack flowregulator is trimmed until the actual pressure value from the pressuresensing arrangement is the stored value.

It will be appreciated that the burner installation and the methods ofoperating and commissioning the burner installation are closely relatedto each other and that features described in respect of the installationmay be adopted in either of the methods, and that features described inrespect of one of the methods may be adopted in the other method or inthe installation.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example an embodiment of the invention will now be describedwith reference to the accompanying schematic drawing, of which:

FIG. 1 is a block diagram of a burner installation.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, a burner installation comprises a fuel burner 1which in this case is a gas and oil burner. Gas is fed along a pipe 2via a pressure regulator 3 and a butterfly valve 4, and oil is fed alonga pipe 5 and a butterfly valve 6. Air is driven along a duct 7 by a fan8 via a damper valve 9 which in this particular example is shown as amulti-vaned damper valve. The burner also has a pilot fuel feed 10.

In the burner 1, the fuel and air are mixed and combustion takes place.The products of combustion pass from the burner 1 through a heatexchanger 11 of a boiler 12 into the flue 14. The combustion productspass up the flue 14 through a stack flow regulator 15, which comprises adamper valve, through an inclined portion 14A of the flue and into avertical stack 16. In FIG. 1, the inclined portion 14A of the flue andthe stack 16 are shown entirely schematically with only end parts of theportion 14A and a bottom part of the stack 16 shown. In this particularexample the regulator 15 is shown as a multi-vaned damper valve.

A control device 20 is provided to control the operation of the burnerinstallation. The control device receives many inputs and controls theoperation of many parts of the installation in a conventional manner; inthe interests of clarity, it is only the control aspects of relevance tothe present invention that will now be described and that are shown inFIG. 1. The butterfly valve 4 controlling the flow of gas to the burner1 is set by a servo motor 21 connected to the control device 20 and ableto receive control signals determining the position adopted by the servomotor 21. The butterfly valve 6 controlling the flow of oil to theburner 1 is set by a servo motor 22 connected to the control device 20and able to receive control signals determining the position adopted bythe servo motor 22. The multi-vaned damper valve 9 controlling the flowof air to the burner is set by a servo motor 23 connected to the controldevice 20 and able to receive control signals determining the positionadopted by the servo motor 23. The stack flow regulator 15 controllingthe flow of combustion products through the stack 16 is set by a servomotor 24 connected to the control device 20 and able to receive controlsignals determining the position adopted by the servo motor 24. Adifferential pressure sensing arrangement 26 is provided with a pressuresensor 28 in the flue 14 and is arranged to measure the difference inpressure from ambient pressure, to which it is exposed, and the pressureat the sensor 28. The sensing arrangement 26 provides an output signalrepresenting that difference in pressure. The output signal is connectedto the control device 20.

The control unit 20 includes a store 30 which is also shown in FIG. 1 inan expanded schematic form. In the expanded part of FIG. 1, the store 30is shown with the left hand column, A, showing the numbered rows fordifferent sets of values. There are then four further columns: the firsttwo of those, B and C, store the settings of the fuel and air valves, asdescribed in more detail in GB 2138610A. In addition there is a furthercolumn, D, that stores respective associated settings of the stack flowregulator 15 for each pair of settings of the fuel and air valves; infurther addition there is a further column, E, that stores a respectiveassociated pressure value for the reading from the differential pressuresensing arrangement 26 for each pair of settings of the fuel and airvalves. As will now be understood, pairs of air and fuel valve settingsare stored, together with an associated setting of the stack flowregulator 15 and an associated value for the pressure differencemeasured by the differential pressure sensing arrangement 26, fordifferent firing rates of the burner. Those settings are generated by acommissioning engineer when the control system for the burner is firstset up.

In operation, when the control system of FIG. 1 is commissioned, thecommissioning engineer not only sets the air and fuel valves to settingsthat provide optimum combustion conditions, but also sets the stack flowregulator to an optimum position. Once the engineer is satisfied thatthe best settings have been achieved for a given firing rate, they arestored in the store 30 along with the pressure difference value from thedifferential pressure setting arrangement 26. The commissioning engineercan then adjust the firing rate of the burner upwards or downwards andstore a set of optimum values for that firing rate. By repeating thatprocess, values can be entered across the full firing range of theburner. If the burner is to operate on only one fuel then thecommissioning can be carried out just with that fuel, but if the burneris also to operate with a second fuel, the commissioning proceduredescribed above can be repeated for the second fuel.

Once the burner has been fully commissioned, it is ready for operation.When the burner is set to a given firing rate, the control device looksup in the store 30 the settings of the servo motors 21, 22, 23 and 24for that firing rate and adjusts them accordingly. The control devicealso looks up the stored differential pressure value corresponding tothe servo motor settings and receives a signal from the differentialpressure setting arrangement 26 of the actual differential pressurevalue. In the event that there is a difference between those twodifferential pressure values, the control device trims the setting ofthe servo motor of the differential pressure setting arrangement 26 toreduce or eliminate the difference.

The boiler installation described above may for example be employed inthe heating system of large premises, for example a factory, offices, ahotel or hospital.

It is also possible for other values to be stored alongside the fourvalues just referred to. For example in WO2012/056228A2, the contents ofwhich are incorporated herein by reference, a modified version of thecontrol arrangement of GB2138610A is described in which respectivevalues of fuel pressure and air pressure upstream of the burner arestored in the store 30 for each pair of fuel and air valve settings.Such values could be stored in a modified version of this invention inaddition to the other values already mentioned.

In GB 2169726A, the contents of which are incorporated herein byreference, the control device 20 is connected to receive a feedbacksignal from an exhaust gas analysis system and that signal is used totrim the air valve setting from the stored value to a slightly differentvalue. That arrangement, with or without the modifications anddevelopments described in WO2012/056228A2, may be employed inembodiments of the present invention.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims.

1. A burner installation comprising a stack and a burner upstream of thestack for burning fuel in air to produce combustion products which arepassed into the stack; a fuel valve for adjusting flow of fuel to theburner; an air valve for adjusting flow of air to the burner; a controldevice including a store arranged to store pairs of values of air andfuel valve settings at various firing rates of the burner and forcontrolling the air and fuel valve settings in dependence upon thestored air and fuel valve settings; a stack flow regulator for adjustingflow of combustion products through the stack; and a pressure sensingarrangement for monitoring pressure of combustion products downstream ofthe burner; wherein the store is arranged for storing respective pairsof values of a setting of the stack flow regulator and a measured valuefrom the pressure sensing arrangement for the pairs of values of air andfuel valve settings; and wherein the control device is arranged toreceive a feedback signal from the pressure sensing arrangement forcomparing an actual pressure value with a stored pressure value and totrim the setting of the stack flow regulator to cause the actualpressure value from the pressure sensing arrangement to move closer tothe stored pressure value.
 2. A burner installation according to claim1, wherein the burner installation further comprises a flue forconveying combustion products from the burner to the stack.
 3. A burnerinstallation according to claim 2, wherein the stack flow regulator isdisposed in the flue.
 4. A burner installation according to claim 1,wherein the stack flow regulator comprises a valve having one or morevanes.
 5. A burner installation according to claim 1, wherein thepressure sensing arrangement comprises a pressure sensor upstream of thestack flow regulator
 6. A burner installation according to claim 5,wherein the pressure sensing arrangement is a differential pressuresensing arrangement and is arranged to measure a pressure differencebetween the pressure sensor upstream of the stack flow regulator andambient pressure.
 7. A burner installation according to claim 6, whereinthe pressure sensing arrangement is connected to the control device toprovide a pressure value representing the difference in pressuremeasured between the pressure sensor upstream of the stack flowregulator and ambient pressure.
 8. A method of operating a burnerinstallation, comprising the following steps: providing a burnerinstallation comprising a stack and a burner upstream of the stack forburning fuel in air to produce combustion products which are passed intothe stack, a fuel valve for adjusting flow of fuel to the burner, an airvalve for adjusting flow of air to the burner, a control deviceincluding a store, a stack flow regulator for adjusting the flow ofcombustion products through the stack, and a pressure sensingarrangement for monitoring pressure of combustion products downstream ofthe burner; storing, at various firing rates of the burner, pairs ofvalues of air and fuel valve settings and associated pairs of values ofa setting of the stack flow regulator and a measured value from thepressure sensing arrangement; operating the burner and controlling theair and fuel valve settings and the stack flow regulator valve settingin dependence upon the stored air and fuel valve settings and theassociated stack flow regulator setting; receiving at the control devicea feedback signal of an actual pressure value from the pressure sensingarrangement; comparing the actual pressure value from the feedbacksignal with a stored pressure value; and trimming the setting of thestack flow regulator to cause the actual pressure value from thepressure sensing arrangement to move closer to the stored value.
 9. Amethod according to claim 8, wherein the pressure sensing arrangementmeasures a pressure difference between a pressure sensor upstream of thestack flow regulator and ambient pressure, and the pressure differenceis a pressure value fed back as a signal to the control device.
 10. Amethod of commissioning a burner installation, comprising the followingsteps: (i) providing a burner installation comprising a stack and aburner upstream of the stack for burning fuel in air to producecombustion products which are passed into the stack, a fuel valve foradjusting flow of fuel to the burner, an air valve for adjusting flow ofair to the burner, a control device including a store, a stack flowregulator for adjusting flow of combustion products through the stack,and a pressure sensing arrangement for monitoring pressure of combustionproducts downstream of the burner; (ii) adjusting air and fuel valvesettings to positions where desired combustion conditions are obtainedfor a, first firing rate of the burner, (iii) storing the pair of valuesof air and fuel valve settings that provide the desired combustionconditions; (iv) adjusting a setting of the stack flow regulator to aposition where, for the first firing rate of the burner, a desired stackflow of combustion products is obtained; (v) storing a value of thesetting of the stack flow regulator and the pressure value from thepressure sensing arrangement with the values of the air and fuel valvesettings; and (vi) repeating steps (ii) to (v) above at other firingrates of the burner.
 11. A method according to claim 10, wherein thepressure sensing arrangement measures a pressure difference between apressure sensor upstream of the stack flow regulator and ambientpressure, and the pressure difference is the pressure value stored. 12.A method according to claim 10, further comprising the followingsubsequent steps: operating the burner, controlling the air and fuelvalve settings in dependence upon the stored air and fuel valvesettings, and setting the stack flow regulator according to the valuestored in association with the air and fuel valve settings; receiving atthe control device a feedback signal of an actual pressure value fromthe pressure sensing arrangement; comparing the actual pressure valuefrom the feedback signal with the stored pressure value associated withthe stack flow regulator setting value; and trimming the setting of thestack flow regulator to cause the actual pressure value from thepressure sensing arrangement to move closer to the stored value.
 13. Amethod according to claim 12, wherein the pressure sensing arrangementmeasures a pressure difference between a pressure sensor upstream of thestack flow regulator and ambient pressure, and the pressure differenceis the pressure value fed back as a signal to the control device.
 14. Amethod according to claim 12, wherein the setting of the stack flowregulator is trimmed until the actual pressure value from the pressuresensing arrangement is the stored value.